In the above-mentioned inverter apparatus, the frequency of an alternating-current output voltage corresponds to the frequency of a drive signal for driving a switching MOS transistor. Accordingly, to gain a stable output voltage having a defined frequency, the MOS transistor must quickly respond to the change in voltage of a drive signal of the defined frequency and carry out the switching operation thereof.
On the other hand, it is generally known that an equivalent input capacitance is exists between a gate and a source of a MOS transistor. Such an input capacitance is determined by the size of the source region, i.e., a diffusion region, and the concentration of impurities therein, a location of the gate and source, and the like, and is parasitically formed when the MOS transistor is formed on a semiconductor substrate.
Accordingly, where an input capacitance (capacitor) exists between the gate and the source of the transistor, a problem arises in that, due to the charging or discharging characteristics of the capacitor, the input voltage of the transistor cannot quickly follow the change in voltage of the aforementioned drive signal. Especially, the higher the frequency of the drive signal, the greater the influence. Accordingly, this problem must be solved, from the viewpoint of acquiring a stable high frequency output voltage. On the other hand, because of the power loss caused by resistors inserted in the input circuit, for compensating the influence of the capacitor, another problem arises in that the efficiency of the power conversion of the whole apparatus is lowered.
Furthermore, it is generally known that an equivalent output capacitance exists between a drain and a source of a MOS transistor. The output capacitance is parasitically formed during the forming of the transistor, as in the aforementioned input capacitance. The existence of the output capacitance (capacitor) causes not only the same problem as that in the aforementioned input capacitor, but also other problems.
The details of the problems arising due to the existence of the parasite input capacitor and parasite output capacitor of the aforementioned MOS transistor will be explained later.